Process of treating cellulose fiber and product of same



Patented a... 26, 1932 UNITED STATES PATENT OFFICE GEORGE A. RICHTER, OF BERLIN, NEW HAMPSHIRE, ASSIGNOR TO BROWN COMPANY,.

OF BERLIN, NEW HAMPSHIRE, A CORPORATION OF MAINE PROCESS OF TREATING CELLULOSE FIBER AND PRODUCT F SAME We hrawing.

tn the various industries in which cellulose is employed as a raw material, it has heretofore been the practice to treat the cellulose in the form of fiber of substantially natural or ori 'inal size. Thus in the re aration of cellulose derivatives such as xanthate, acetate, nitrate, etc., cotton fiber or fiber liberated from Wood is treated substantially in the same size as it is found in nature.

It Uwing to the widely varying sizes of cellulose fibers as they occur in nature, it is sometimes inefiicient to process cellulose fiber in its natural condition. For instance, in manufacturing rayon by the viscose-rayon rt process, it has been the practice to treat cellulose fiber with caustic soda solution, and then to age the treated fiber to effect its depolymerization for Xanthation. In order to efiect a substantially complete Xanthation cc of the fiber, it is necessary to effect a thorough depolymerization of substantially all the liher. llnasmuch as the longer and thicker fibers require a longer aging period than the smaller fibers, a long aging period is necessary .to effect the desired complete depolymerization; and, in such case, the small fibers are depolymerized more than the larger ones, frequently being over-depolynierized. The aged fiber is thus made up of fibers depolyer merized to widely varying degrees.

ln accordance with the present invention, cellulose fiber as it is obtained from nature is materially reduced in size prior to use or to chemical treatment, thereby producing a raw material of much greater chemical reactivity and which hencereacts much more rapidly and completely when treated with chemical reagents. Such size reduction is particularly advantageous in the viscose-rayon process,

as l have found that by materially reducing the fiber in size prior to processing, the aging period may be greatly reduced, if not entirely eliminated, and a substantially uniformly depolymerized product obtained. I have also found that by so doing it am enabled to 5ft tion more rapidly, and Xanthates the soda Application filed June 2, 1927. Serial No. 196,135.

cellulose thus produced more, readily and completely. Reduction of the original fiber to materially smaller size may be accomplished expediently by beating, but this operation need not be carried out under conditions to effect its hydration, as is customary in papermaking.

A process such as described may be applied to great advantage in treating cellulose fiber of high average fiber length,-for example, the long fiber portion of a high alpha cellulose Wood fiber. Such long fiber portion is notably free from specks, colloidal coloring material, resin, ash, and other contaminations, and is hence eminently suitable for derivative preparation, but heretofore the use of such fiber involved an especially long and troublesome aging period.

A better understanding of the process of the present invention may be obtained from the following more complete description thereof, which relates to viscose-rayon processing of a high alpha-cellulose wood fiber, which for convenience of designation will hereinafter be termed alpha wood fiber. It is to be understood, however, that my invention may be applied to the preparation of other derivatives and to other wood fiber, such as snlphite fiber, or to cellulose fiber of other derivations, such as cotton fiber. An alpha wood fiber such as I employ may be prepared by the process disclosed in application, Serial No. 716,154, filed May 27, 1924, by Milton 0. Schur and myself. In accordance with that process, chemical wood fiber, such as sulphite pulp, is subjected to a series of chemical treatments, including an initial treatment with chlorine water, followed by digestion in an alkaline liquor and a final bleaching treatment, which effect a removal of non-alpha cellulose components therefrom to produce a white fiber of high alpha cellu= lose content and especially low in impurities such as lignin, resins, pentosans, and oxycelluloses. More particularly, as described in that application for patent, the unbleached sulphite pulp is initially treated for about thirty minutes as a stock suspension with 0.3% to 0.6% of chlorine, or with 1% to 2% of hypochlorite bleach, based on the weight of dry pulp. The pulp is then washed and digested from two to six hours at elevated temperature in an alkaline liquor of a strength of 0.1% to-0.5% caustic soda, or from 1% to 5% caustic soda, based on dry pulp. The plup is again washed and then treated in the form of a suspension at a temperature of about 80 F. and for from six to eight hours with 2% to 4% of hypochlorite bleach, based on dry pulp, whereupon the bleached product is thoroughly washed and treated with suitable antichlor, such as calcium bisulphite, to neutralize any bleach that may remain in the product.

If desired, the long fiber portion, which yields rayon of the highest quality, may beselected from the rest of the fiber and then treated by my process, but obviously all the fiber may be so treated. In accordance with my process, the fiber is materially reduced 1n size, as by beating, but this operation need effect only a shortening or cutting. of the fiber, as, I am not especially interested in effecting its hydration, as is desired by the papermaker, nor in producing paper having good physical characteristics. Thus, beating may even be effected in a jordan or in a hollander in which the beater roll is provided with very sharp blades set to clear the bedplate only slightly, and may even be carried out at elevated temperature,this being undesirable in usual papermaking procedure, as elevated temperature tends to decrease the hydratability of cellulose fiber. The 'beatin is preferably continued until the origina fiber has been considerably reduced in average fiber length and width. Thus, a typical alpha wood fiber having an average fiber length of," say, from 0.7 to 1.3 mm. may be beaten until its average fiber length has been reduced to below 0.2 mm.

The shortened fiber ma then be run off into the so-called drier s eet usually supplied to rayon manufacturers, but preferably,-

however, it is run off into waterleaf paper, as described in my application, Serial No. 194,506, filed May 26, 1927, wherein the advantages of processing fiber of short length in paper form are disclosed. The shortened fiber is of notably lower viscosity than the original fiber, this quality apparently denoting depolymerization. Thus, the shortened fiber requires little, if any, aging rior to xanthation, whereas the original ber re quires considerable aging to acquire the same viscosity and reactivity.

K The viscose-rayon processing of such reduced fiber may be carried out substantially as follows: the drier sheet or paper composed .of the reduced fiber is saturated with caustic soda solution, as usual, to effect a conversion of the fiber into soda cellulose.- Inasmuch In such case verted into soda cellulose. After the excess solution has been removed from the drier sheet or paper, it is shredded into crumby flocks, which may be xanthated with little, if any, aging. -'lhe xanthated fiber dissolvesquite readily in caustic soda solution to produce a xanthate solution suitable for spinning and containing little unxanthated fiber. By the process of the present invention, I am thus enabled to eliminate or, in'any event, to shorten considerably, the usual aging period of from 48 to 120 hours. I am also enabled to obtain a substantially uniformly depolymerized fiber for xanthation.

The reduction of the fiber may, if desired, becontinued by beating or other mechanical treatment until it has been reduced to a pulverulent condition and can no longer be sheetedbut must be handled and treated in bulk form as'in the form of bulk powder or compressed cakes, or in the form of a suspension, in water or other liquid vehicle. lnasmuch as cellulose in such conditionhas a very large aggregate surface, it is exceedingly reactive and may hence be converted into cellulose xanthate or other cellulose derivatives very rapidly and completely. Furthermore, it is adapted for other uses requiring substantially pure cellulose in non-fibrous condition. Thus, when preparedfrom cotton fiberor from a wood fiber such as- 1 alpha fiber, it consists essentially of alpha cellulose only, and may hence serve as a raw material not only for the preparation of- Y which passes through a IOO-mesh screen, it

is necessary to pulverize or to complete pul- 1 verization in apparatus other than a beater. pulverization may, for instance, be ,efiected by passing the dry fiber, partly reduced by beating if desired, through a suitable ball or roller mill, which serves to pound or grind the fibers into a finely divided powder.

The powder may be separated from residual coarse particles or fiber, as by air flotation, and the coarse particles or fiber returned to the mill for re 'rinding. If it is desired to pulverize the fiber by a wet process, it is preferable either to convert the fiber to a non-hydratable condition or to pulverize in a non-hydrating wetting medium, as hydration of the fiber appears to hinder its pulverization. Thus, the fiber may be mercerized or converted into re' enerated cellulose fiber, in which case pu verization may be performed in the presence of water, as I mercerized or regenerated cellulose fiberis non-hydratable. Or the hydratable fiber may be pulverized in a wetting medium such ill as alcohol or benzol, which is of a non-hydrating character.

In some of the appended claims, I speak of individualized cellulose fibers, by which expression i mean fibers in a separate or individual condition, as obtains in the case of wood pulps or cotton, as distinguised from the condition of the fiber in wood, nut shells, or the like, where they are bound together as a rigid mass of cementitious material. l fhile it is easy to grind a rigid mass such, as wood or nut shells into a powder, neverthe less the treatment of the powder with chemical solutions such as those of alkali to dissolve out non-alpha cellulose components is accompanied by a vastly greater loss of alpha cellulose than is the case when the fibers are fil'st liberated from the cementitious material and then mechanically reduced as separated or individualized fibers.

By the term cellulose fiber as employed herein and in the appended claims, ll mean not only a substantially pure form of cellulose such as cotton fiber or a refined wood fiber composed essentially of alpha cellulose,

but also the usual commercial wood fibers, e. g., sulphite fiber, which, in addition to alpha cellulose, contain a certain small proportion of non-alpha cellulose components such as pentosans, beta and gamma celluloses, oxycelluloses, and the like, but which have an alpha cellulose content materially above 00%.

In carrying out the shortening or reduction of the fiber as in a powder engine or in a ball mill, as hereinbefore described, it is clear that the fiber is in the form of a mass in which the fiber units are in random arrangement. in other words, the process or my invention does not require that the fiber used as a raw material be subjected to special manipulation designed to produce a particular fiber arrangement or formation, for instance, parallelism of fiber units, such as is brought about when cutting fibers are subjected to the action of carding machines.

I do not herein claim specifically the subject matter of applica tion, Serial No. 122,271, filed July 13, 1926, which discloses the beating or hydration of cellulose fiber prior to viscose-rayon processing, or the subject matter of application, Serial No. 194,506, filed May 26, 1927, which discloses the advantages of using waterleaf paper composed of reduced fiber. Nor do I herein claim the subter of its continuation application Serial No. 97,998, filed March 27 1926, by Milton 0. Schur, Royal H. Rasch and myself, wherein the advantages of beating cellulose fiber prior to nitration are disclosed, or the subject matter of its continuation application, Serial No. 140,674, filed October 9, 1926.

What I claim is:

1. A process which comprises beating eel, lulose fiber below an average fiber length of 0.2 mm. while maintaining it substantially free from chemicals, and then converting the reduced fiber into a cellulose derivative.

2. A rocess which comprises beating cellulosic her until its average fiber length has been shortened to below 0.2 mm. while maintaining it substantially free from chemicals, and then converting such beaten fiber into cellulose xanthate.

3. A process which comprises materially reducing cellulosic fiber in size while maintaining it substantially free from chemicals, then treating such reduced fiber with caustic soda solution, aging the treated fiber for only zfiitshort period, and then Xanthating the aged 4. A step which comprises pulverizing cellulose fiber in the presence of a non-hydrating wetting medium.

5. A product consisting of mechanically pulverized wood substantially free from none alpha cellulose components.

6. A process which comprises converting a product consisting of mechanically pulverized wood fiber substantially free of nonalpha wood components into cellulose derivative.

In testimony whereofI have afiixed my signature.

GEORGE A. RICHTER. 

